1. Field of the Invention
The present invention relates to an adaptive antenna receiving apparatus and, more particularly, to an adaptive antenna receiving apparatus which receives a CDMA (Code Division Multiple Access) signal and adaptively forms an antenna directional beam to receive a desired wave and also removes interference.
2. Description of the Prior Art
CDMA is expected as a radio access scheme for a mobile communication cellular system of next generation because of its capability of increasing the subscriber capacity. However, on the base station receiving side, simultaneously accessing user signals interfere with each other. To remove interference between user signals, an adaptive array antenna has been proposed.
An adaptive array antenna receives signals using a plurality of antennas, and weights and combines the received signals using complex numbers. Next, the adaptive array antenna forms a directional beam by controlling the amplitude and phase of the reception signal of each antenna. With this operation, only a desired user signal can be received. Additionally, any other user interference signal can be suppressed.
Two methods of determining the antenna weight of an adaptive antenna have been generally known.
As one method, a weight is determined by feedback control using an adaptive update algorithm such as LMS (Least Mean Square) or RLS in accordance with the MMSE (Minimum Mean Square Error) (feedback control method).
The other is an open loop control method in which the direction of arrival of a desired wave is estimated from an antenna reception signal by using an arrival direction estimating algorithm such as MUSIC or ESPRIT, and a beam is directed to that direction.
This open loop control method has an advantage that the antenna weight can be accurately calculated even from a short reception signal sequence, unlike the feedback control method. However, the arithmetic amount becomes large.
Japanese Unexamined Patent Publication No. 11-274976 has proposed xe2x80x9cArray Antenna System at Radio Base Stationxe2x80x9d which uses a method of easily determining an antenna weight without using any complex arrival direction estimating algorithm in the open loop control method.
FIG. 1 shows an adaptive antenna receiving apparatus according to this prior art. This adaptive antenna receiving apparatus has L (L is a positive integer) path signal processing means 101-1 to 101-L. As the number L, a number corresponding to a multipath transmission path in a mobile communication environment, i.e., the number of paths is employed such that the path signal processing means receive and demodulate CDMA signals.
The path signal processing means 101-1 to 101-L have antenna weight calculation means 102-1 to 102-L, beam formers 103-1 to 103-L, and RAKE combining/weighting means 104-1 to 104-L, respectively. The path #1 signal processing means 101-1 will be described below. The description also applies to the path #2 signal processing means 101-2 to path #L signal processing means 101-L.
The antenna weight calculation means 102-1 has an antenna signal in-phase averaging means 106-1, correlation-to-reference-antenna detection means 107-1, and time averaging means 108-1.
The antenna signal in-phase averaging means 106-1 improves the SINR by matching the phases of despread symbols of the respective paths and adding their vectors.
This operation cannot be performed when the symbols are modulated. However, in-phase addition can be done after modulation is canceled by a known pilot symbol using a pilot signal. The larger the number of symbols for in-phase averaging becomes, the more the SINR can be improved. However, it is limited if a quick phase variation is present due to fading or the like.
The antenna signal in-phase averaging means 106-1 can employ an arbitrary number of symbols to be averaged and an arbitrary method of weighting each symbol.
The correlation-to-reference-antenna detection means 107-1 detects the correlation between a reference antenna reception signal and the remaining antenna reception signals. More specifically, the correlation-to-reference-antenna detection means 107-1 multiplies the reception signal of another antenna by the complex conjugate signal of the reference antenna reception signal.
For example, antenna No. 1 is defined as a reference antenna. The output from the correlation-to-reference-antenna detection means 107-1 is given by
R(i,j,m)=ZEL(i,j,m)Z*EL(i,1,m)xe2x80x83xe2x80x83(1)
where i (i is an integer; 1xe2x89xa6ixe2x89xa6L) is the path number, j (j is an integer; 2xe2x89xa6jxe2x89xa6N) is the antenna number, and m (m is a positive integer) is the output number of an output ZEL(i,j,m) from the antenna signal in-phase averaging means 106-1.
FIG. 6 shows signals received by array antennas 61-1 to 61-N (N is a positive integer). The signal received by each antenna has a phase lag depending on its direction of arrival. For example, the signal received by the antenna element 61-1 (reference antenna element) has a phase lag of (jxe2x88x921)(2xcfx80d/xcex)sin xcfx860 with respect to the signal received by the jth antenna element 61-j (j is an integer; 1 less than jxe2x89xa6N). In this case, xcfx860 is the direction of signal arrival, d is the interval between adjacent antennas, and xcex is the signal wavelength.
Hence, the phase of R(i, j, m) is ideally detected as (jxe2x88x921)(2xcfx80d/xcex)sin xcfx860.
The time averaging means 108-1 averages a plurality of outputs from the correlation-to-reference-antenna detection means 107-1. An arbitrary time and method can be employed as an averaging time and weighting method to be used for this averaging. An output from the time averaging means 108-1 is an antenna weight w(i,j,m).
The beam former 103-1 weights and combines the respective antenna reception signal using the antenna weights w(i,j,m) output from the time averaging means 108-1. That is, using the antenna weights calculated by the antenna weight calculation means 102-1, despread signals are received by antenna directional beams for the respective paths.
FIG. 4 shows the arrangement of the beam former 103-1 of path #1. The number of antennas is N (N is a positive integer).
The beam formers 103-1 to 103-L have complex conjugate means (41-1-1 to N) to (41-L-1 to N), multipliers (42-1-1 to N) to (42-L-1 to N), and combiners 43-1 to 43-L, respectively.
Each of the complex conjugate means 41-1-1 to 41-1-N calculates a complex conjugate w*(i, j, m) of the antenna weight w(i,j,m) (j in the antenna weight w and its complex conjugate w* is an integer; jxe2x89xa71).
Each of the multipliers 42-1-1 to 42-1-N multiplies a corresponding despread input in path #1 by the complex conjugate w*(i, j, m) of the antenna weight.
The combiner 43-1 adds the outputs from the multipliers 42-1-1 to 42-1-N, thereby calculating the beam former output.
The phase of the complex conjugate w*(i,j,m) of the antenna weight is ideally xe2x88x92(jxe2x88x921)(2xcfx80d/xcex)sin xcfx860. Hence, the beam former 103-1 acts to combine signals that have arrived from the direction xcfx860 such that the reception signals of the respective antennas and the reception signal of the reference antenna element 61-1 are in phase. In addition, since a signal that has arrived from a direction different from the direction xcfx860 is not in phase, a beam that has a gain in the direction xcfx860 and reduces gains in directions other than xcfx860 can be formed.
The RAKE combining/weighting means 104-1 compensates for a variation in phase of the output from the beam former 103-1, i.e., phase of the reference antenna and weights the output to combine the paths (RAKE combining). That is, the RAKE combining/weighting means 104-1 weights the beam output of each path. This weighting is executed such that the SINR (Signal to Interference and Noise Ratio) after combining is maximized.
The combiner 105 adds the weighted outputs of the respective paths to obtain a demodulated output. That is, the combiner 105 adds the outputs from the path signal processing means 101-1 to 101-L, thereby obtaining a high-quality demodulated output.
In the above-described conventional adaptive antenna receiving apparatus, however, the phases of the reception signals of the respective antennas can be made to match the phase of the reference antenna only when the averaging time of the antenna signal in-phase averaging means 106-1 to 106-L or time averaging means 108-1 to 108-L is sufficiently long. That is, only in this case, the beam center can be directed to the signal arrival direction xcfx860.
That is, if the averaging time is short, the phase accuracy of the antenna weight degrades due to interference or noise. For this reason, the beam center direction shifts. In addition, the interference suppression characteristic outside the beam band also largely degrades.
The present invention has been made in consideration of the above problems of prior art, and has as its object to provide an adaptive antenna receiving apparatus which obtains an additional averaging effect by detecting the correlations between adjacent antennas for all antennas and adding them, and also obtains an excellent interference suppression characteristic outside a beam band with little shift in beam center direction by using a fixed beam weight as an antenna weight even when the averaging time of antenna weight calculation is short.
In order to achieve the above object, according to the first aspect of the present invention, there is provided an adaptive antenna receiving apparatus which receives a CDMA (Code Division Multiple Access) signal by an array antenna, adaptively forms a directional beam to receive a desired wave, and suppresses interference, wherein a plurality of correlations between adjacent antennas are detected for each path, a fixed beam unique to each path arrival direction of the desired wave is formed on the basis of a vector generated by averaging the plurality of detected correlations, and each path is received and combined.
In order to achieve the above object, according to the second aspect of the present invention, there is provided an adaptive antenna receiving apparatus which receives a CDMA (Code Division Multiple Access) signal by an array antenna, adaptively forms a directional beam to receive a desired wave, and suppresses interference, wherein a plurality of correlations between adjacent antennas are detected for each signal sequence despread with a plurality of chip timings, a fixed beam unique to an arrival direction of each signal sequence is formed on the basis of a vector generated by averaging the plurality of detected correlations, and a path timing is detected on the basis of a delay profile generated from an output of each signal sequence.
In order to achieve the above object, according to the third aspect of the present invention, there is provided an adaptive antenna receiving apparatus which receives a CDMA (Code Division Multiple Access) signal by an array antenna, adaptively forms a directional beam to receive a desired wave, and suppresses interference, wherein a plurality of correlations between adjacent antennas are detected for each signal sequence despread with a plurality of chip timings, a fixed beam unique to an arrival direction of each signal sequence is formed on the basis of a vector generated by averaging the plurality of detected correlations, a path timing is detected on the basis of a delay profile generated from an output of each signal sequence, and each path is received and combined using the path timing and the fixed beam at the path timing.
In order to achieve the above object, according to the fourth aspect of the present invention, there is provided an adaptive antenna receiving apparatus wherein an antenna weight of the fixed beam in any one of the above first to third aspects is generated to give 0 phase shift to a reception signal at a geometrical center of the array antenna.
In order to achieve the above object, according to the fifth aspect of the present invention, there is provided an adaptive antenna receiving apparatus which receives a CDMA (Code Division Multiple Access) signal by an array antenna, adaptively forms a directional beam to receive a desired wave, and suppresses interference, comprising antenna signal in-phase averaging means, arranged for each path, for in-phase-averaging a despread signal of each antenna, adjacent antenna correlation detection means for detecting correlation between adjacent antennas for each output of the antenna signal in-phase averaging means, antenna correlation averaging means for averaging outputs from the adjacent antenna correlation detection means, time averaging means for time-averaging outputs from the antenna correlation averaging means, normalization means for normalizing an output from the time averaging means, fixed beam weight generation means for fixing an output from the normalization means, a beam former for executing beam forming for the despread signal using an output from the fixed beam weight generation means, RAKE combining/weighting means for weighting using an output from the beam former and the output from the fixed beam weight generation means, and a combiner for combining outputs from the RAKE combining/weighting means of respective paths and outputting a demodulated signal.
In order to achieve the above object, according to the sixth aspect of the present invention, there is provided an adaptive antenna receiving apparatus which receives a CDMA (Code Division Multiple Access) signal by an array antenna, adaptively forms a directional beam to receive a desired wave, and suppresses interference, comprising a sliding correlator for outputting a signal sequence obtained by dispreading a reception signal with a plurality of chip timings, antenna signal in-phase averaging means, arranged for each signal sequence, for in-phase-averaging a signal of each antenna, adjacent antenna correlation detection means for detecting correlation between adjacent antennas for each output of the antenna signal in-phase averaging means, antenna correlation averaging means for averaging outputs from the adjacent antenna correlation detection means, time averaging means for time-averaging outputs from the antenna correlation averaging means, normalization means for normalizing an output from the time averaging means, fixed beam weight generation means for fixing an output from the normalization means, a beam former for executing beam forming for the despread signal sequence using an output from the fixed beam weight generation means, delay profile generation means for generating a delay profile from an output from the beam former, and path timing detection means for detecting a path timing from the delay profile.
In order to achieve the above object, according to the seventh aspect of the present invention, there is provided an adaptive antenna receiving apparatus which receives a CDMA (Code Division Multiple Access) signal by an array antenna, adaptively forms a directional beam to receive a desired wave, and suppresses interference, comprising a sliding correlator for outputting a signal sequence obtained by dispreading a reception signal with a plurality of chip timings, antenna signal in-phase averaging means, arranged for each signal sequence, for in-phase-averaging a signal of each antenna, adjacent antenna correlation detection means for detecting correlation between adjacent antennas for each output of the antenna signal in-phase averaging means, antenna correlation averaging means for averaging outputs from the adjacent antenna correlation detection means, time averaging means for time-averaging outputs from the antenna correlation averaging means, normalization means for normalizing an output from the time averaging means, fixed beam weight generation means for fixing an output from the normalization means, a first beam former for executing beam forming for the despread signal sequence using an output from the fixed beam weight generation means, delay profile generation means for generating a delay profile from an output from the first beam former, path timing detection means for detecting a path timing from the delay profile, a second beam former arranged for each path to receive each path using the path timing and a fixed beam at the path timing, RAKE combining/weighting means for weighting an output from the second beam former, and a combiner for combining outputs from the RAKE combining/weighting means of respective paths and outputting a demodulated signal.
In order to achieve the above object, according to the eighth aspect of the present invention, there is provided an adaptive antenna receiving apparatus wherein the fixed beam weight generation means of any one of the above fifth to seventh aspects generates an antenna weight of a fixed beam to give a 0 phase shift to a reception signal at a geometrical center of the array antenna.
As is apparent from the above aspects, according to the present invention, an additional averaging effect is obtained by detecting a plurality of correlations between adjacent antennas and adding them. In addition, as an antenna weight, a fixed beam weight that sets the geometrical center of the antenna at 0 phase shift is used. Hence, an excellent interference suppression characteristic outside the beam band with little shift in beam center direction can be realized even when the averaging time of antenna weight calculation is short.
In the present invention, antenna weights are calculated in a short time by open loop control simultaneously with calculation of each path timing, and each path timing is detected using a beam-formed signal, thereby realizing an excellent path timing detection characteristic.
Additionally, in the present invention, when the demodulation/reception section executes beam forming using the antenna weight of a corresponding path timing in antenna weights used by the path timing detection section, the demodulation/reception section need not newly calculate antenna weights.